In the manufacture of fibers from molten material, such as molten glass, it is normal practice to use electrically resistance heated fiberizing bushings which, in a simplified description, are electrically heated, open top boxes made of a well known precious metal alloy such as platinum/rhodium and having a plurality of nozzles in a bottom plate through which the molten material flows through to form molten meniscuses from which fibers are drawn. An electrical current is passed through each precious metal alloy bushing to heat the bushing and the molten glass flowing into the bushing. The bushings have one or more electrical connectors or ears on each end of the bushing to which is attached a water cooled terminal connector in a known manner. Such bushings are described in detail in U.S. Pat. Nos. 4,740,224 and 6,196,029.
The terminal connector is typically water cooled to protect the copper metal of the terminal connector from the high temperature, usually in the range of 2000 to about 2400 degrees F. of the endwall and tip plate of the bushing. A typical terminal connector is described in detail in U.S. Pat. No. 4,294,502.
Because the terminal connector is water cooled and thus at a temperature much lower than end plates of the bushing, the terminal connectors have a substantial cooling effect on the endwalls of the bushing, the end portions of the tip plate and the glass in the end portions of the bushing. The farther away from the endwall of the bushing that the terminal connector is attached to the bushing ear, the lower the cooling effect on the endwall, and vice versa. Because of differing environmental conditions surrounding each bushing and the different temperatures of the glass flowing into each bushing from the forehearth, it is necessary to be able to adjust the position of the terminal connectors along the length of the bushing ears to obtain a the best uniformity of temperature profile along the length of the bushing tip plate practical. Tip plate temperature uniformity is most important to fiberizing efficiency, to both time and material efficiency.
It is conventional to water cool the terminal connector to protect the copper metal it is made of from overheating and deforming. This cooling of the terminal ear has a detrimental cooling effect on the terminal ear of the bushing and must be offset by the electrical heating of the ear. It is well known that the cross sectional area of the precious metal terminal ear has an effect on the amount of cooling and heating of the ear by the electrical current passing through the ear at the point of connection, which heating must more than offset all of the cooling effect of the cold terminal connector. It has been common practice in the past to taper the ear or ears on each end of the bushing such that as the distance from the unattached end of the ear increases, the cross sectional area of the ear also increases. This can be seen in the bushings described in detail in U.S. Pat. Nos. 4,272,271, 6,065,310, 6,070,437 and 6,196,029.
One problem that often occurs with this type of ear is cold corners of the tip plate because this ear design does not distribute the current uniformly to the end wall and tip plate insufficient power is distributed to the corners of the end wall and tip plate. In these ear designs, it often occurs, and most frequently in developmental bushings or newly developed bushings, that the range of adjustment provided by these prior art ear designs is inadequate and does not allow one to achieve a uniform temperature profile across the length of the tip plate. A bushing ear design having a greater range of adjustment is therefore needed to minimize “cold corners” in the orifice plate or tip plate and to provide an improved temperature profile over the entire orifice plate or the tip plate of the bushings.